The Fin Whale (Balaenoptera physalus), also known as the finback whale, is the second-longest cetacean after the blue whale, reaching lengths of up to 26 m (85 ft) and weights of 77 to 81 tonnes. Its long, slender body is brownish-gray with a lighter underside for countershading.
There are at least two recognized subspecies, one in the North Atlantic and another in the Southern Hemisphere. Fin whales inhabit all major oceans, preferring temperate and cool waters, and primarily feed on smaller fish, squid, and crustaceans. They usually mate in temperate waters during winter and are often seen in pods of 6–10, communicating with frequency-modulated sounds.
Historically targeted by whalers, over 725,000 fin whales were taken from the Southern Hemisphere between 1905 and 1976, leading to significant declines in population. As of 2018, the fin whale is assessed as vulnerable by the IUCN. Adult males average about 21 m (69 ft) and females 22 m (72 ft), demonstrating sexual dimorphism, with females generally larger.
The fin whale is brownish to dark or light gray dorsally and white ventrally. The left side of the fin whale’s head is dark gray, while the right side features a complex pattern of light and dark markings. The lower jaw is typically white or light gray, occasionally extending onto the upper jaw, and dark areas of pigment known as “flipper shadows” are found below the pectoral fins.
Fin whale penises can reach up to 1.3 meters in length, with testes weighing 1–3 kg in mature individuals. Their extensible oral cavity aids in feeding.
Fin whales are found in all major oceans, favoring temperate and cool waters but avoiding polar ice pack regions and some smaller seas. They have a widespread distribution in the North Atlantic, from the Gulf of Mexico and Mediterranean Sea to Baffin Bay and Spitsbergen, with a higher prevalence north of 30°N latitude.
In the North Pacific, they frequent offshore waters from central Baja California to Japan and the Chukchi Sea. Densities peak in the Gulf of Alaska and southeastern Bering Sea between May and October. Some fin whales appear to winter in Hawaiian waters.
Migration patterns remain unclear. North Atlantic fin whales migrate south in autumn from the Labrador-Newfoundland region toward the West Indies, with some populations staying year-round in high latitudes. In the Pacific, southern fin whales migrate from Antarctic feeding grounds to low-latitude breeding areas in winter, though the exact breeding locations are still unknown.
Populations of fin whales in the Mediterranean have preferred feeding areas that overlap with high concentrations of plastic pollution and microplastics, likely due to both being found near high trophic upwelling zones.
Before whaling, the North Pacific fin whale population was estimated at 42,000 to 45,000. Surveys from the 1990s and early 2000s reported between 1,600 and 3,200 off California and approximately 500 in British Columbia in 2004 and 2005. There are signs of fin whales returning to British Columbia, with a sighting in Johnstone Strait in 2011.
Fin whales are also abundant along the coasts of Peru and Chile, particularly in the Los Lagos region and areas like Punta de Choros and Caleta Zorra. They may have possible resident populations in northern and central Chile. In the Northern Indian Ocean and Bay of Bengal, sightings and historical records exist along Sri Lanka, India, and Malaysia.
The fin whale is a filter-feeder that primarily consumes small schooling fish, squid, and crustaceans, including krill and copepods. In the North Pacific, they mainly feed on species such as krill from the genera Euphausia, Thysanoessa, and Nyctiphanes, as well as small fish like Engraulis and Mallotus. Stomach content analysis of fin whales caught from 1952 to 1971 found that 64.1% contained only krill, while smaller percentages contained copepods, fish, and squid.
In British Columbia (1963-1967), euphausiids dominated their diet, and in California (1959-1970), major food sources included Euphausia pacifica and northern anchovy. In the North Atlantic, fin whales primarily consume krill and small fish, with 96% of examined stomachs in Iceland containing krill.
In the Southern Hemisphere, whales primarily feed on krill, especially Euphausia and Thysanoessa, with some consuming fish and amphipods. They swim at about 11 km/h (6.8 mph), gulping up to 70 m³ (18,000 US gal) of water, then push it out through their baleen, capturing prey in the process. Each whale has 262 to 473 baleen plates made of keratin, measuring up to 76 cm (30 in) long.
Typically diving over 200 m (660 ft), they lunge four times to accumulate up to 10 kg (22 lb) of food per gulp. An adult whale can eat up to 1,800 kg (4,000 lb) daily, feeding about three hours a day, similar to human feeding patterns. If food isn’t dense or is too deep, they spend more time searching. One technique involves circling fish schools at high speed to corral and consume them effectively.
